Upgrade 2.4 - GRE MTU

  • Hi,

    Was running the latest 2.3.x version and did an upgrade to 2.4 last night.

    After the upgrade, everything worked fine except OSPF - all neighbours was stuck in varations of "ex" states. After some googling, I learned that this is usually caused by MTU missmatch.

    All neighbours run MTU 1476 on GRE which seems to be standard (they are all still running 2.3.x).

    When I checked "routes" in my Pfsense GUI it listed all GRE interfaces MTU as 1476.
    When I checked ifconfig through shell, it listed all GRE interfaces MTU as 1500.

    Changing MTU manually to 1476 for all GRE instances and voila, OSPF instantly works again.

    Has anyone else who use OSPF and GRE tunnels run into this issue?

    EDIT: Reported as bug by someone else, https://redmine.pfsense.org/issues/8115

  • same here. GRE under ipsec. I setup a cronjob every minute correcting the mtu when needed, my tunnels are up now. I'm running 2.4.2.

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